1. Field of Invention
The present invention relates to optics and materials for variable retardation. The present invention is also related to the application of variable retardation to the adjustment of light pathlengths in optical devices such as kernels and prism assemblies of video projection devices, and particularly to adjustment of multiple light pathlengths to target values.
2. Discussion of Background
Light Engines are utilized in optical devices, particularly projection video devices, and generally comprises a light source, condenser, kernel (prism assembly and microdisplays), and projection lens. A display screen and related electronics, for example, are added to produce a video display product. Many different kernels and prism assemblies are commercially available in varying configurations. However, the kernel is the optical heart of the light engine, and is composed of the prism assembly and at least one, and typically three, LCOS microdisplays.
The function of the components of an LCOS based video projector 100 is explained by example of a light engine with reference to FIG. 1. As shown, white light 110 is generated by a light source 105. The light is collected, homogenized and formed into the proper shape and otherwise processed by optics (not all shown for clarity). The light then enters a prism assembly 150 where it is polarized and broken into red, green and blue polarized light beams. A set of reflective microdisplays 152A, 152B, and 152C are provided and positioned to correspond to each of the polarized light beams (the prism assembly 150 with the attached microdisplays is called a kernel). The beams then follow different paths within the prism assembly 150 such that each beam is directed to a specific reflective microdisplay. The microdisplay that interacts with (reflects) the green beam modulates the green content of a full color video image. Similarly, the red and blue contents of the full color image are modulated by corresponding “red” and “blue” microdisplays. The prism assembly 150 then recombines the modulated beams into a modulated white light beam 160 that contains the full color video image. The resultant modulated white light beam 160 then exits the prism assembly 150 and enters a projection lens 165. Finally, the image-containing beam (white light beam 160 has been modulated and now contains the full color image) is projected onto a screen 170.